I _think_ he meant using for instance fmaa and fs, while the AI is still using um and vanilla spears...

But Timur pretty much summed it up for me, as well. Another main reason I play High is that some of the starting positions are more challenging and more interesting than in Early, and slightly less predictable: see the starting positions of the French or Byzantines, the English-French situation is more entangled than in Early, and you have the very very nice Mongol invasion in 25 years after starting the game, which is yet another factor adding to the flavor and unpredictability...especially if you're playing an Eastern faction, and the GH will actually attack you. 25 years is definitely not enough to take on the horde head on, whereas starting in Early allows you to even finish the game before they arrive...or alternatively meet them with a huge army and wipe them out in one turn (which can be nice, but where's the challenge ?)